High-speed 3D shape measurement of transparent objects by sequential thermal fringe projection and image acquisition in the long-wave infrared

Abstract

Recently, we have successfully tackled the challenge of measuring the 3D shape of uncooperative materials, i.e., materials with optical properties such as being glossy, transparent, absorbent, or translucent. By projecting sequential thermal fringes in the long-wave infrared (LWIR) combined with a stereo camera setup in the midwave infrared (MWIR), we were able to three-dimensionally record object shapes within one second. However, in many applications, e.g., for 100 % quality assurance, even shorter measurement times are required. To achieve camera frame rates higher than 125 fps at room temperature, Max Planck’s law of thermal emission teaches us a change in the camera spectral range from MWIR to LWIR. If irradiation and image acquisition have to run in parallel, the camera chips must therefore be protected against the radiation projected by the CO2 laser at a wavelength of 10.6 µm. Appropriate filters have been available only recently. In this contribution, we present our high-speed LWIR 3D sensor. The work includes a characterization of our setup regarding its measurement accuracy and speed. The results are compared to the performance of previous thermal 3D sensors. We show 3D measurement results of static objects as well as of a dynamic measurement situation of a transparent object. Furthermore, we demonstrate that our setup enables us to extend the measurability of material classes towards objects with high thermal conductivities.

TranSpec3D: A Novel Measurement Principle to Generate A Non-Synthetic Data Set of Transparent and Specular Surfaces without Object Preparation

“…Currently, the mid-wave infrared (MWIR) cameras (sensor 1 ) at 125 fps are the limiting component to also capture dynamic objects. The use of high-speed LWIR cameras at 1000 fps handles this limitation and shows a dynamic measurement process of a crushing bottle with a 20 fps 3D rate [46].…”